Gellan gum is an anionic, linear polysaccharide from microorganisms having a molecular weight of up to 2˜3×105 daltons. The bacterium for producing gellan gum was originally called as Pseudomonas elodea, and later identified as a gram-negative and aerobic bacillus, i.e., Sphingomonas paucimobilis, based on the characteristics of r-RNA and the fact that the bacterium contains the glycolipid sphingosine. It can be said that gellan gum is one of the best thickening agents and one of the best stabilizers at present, based on the excellent properties, and also has a good gelation nature. The gel from gellan gum is easy to use, and has a good flavor-releasing characteristic, and has a high stabilization to heat. In addition, the gel is easy to melt in mouths, and has a high transparence. The time and temperature for gelation are controllable, and the gelation is not easy to be influenced by the variations of pH. The product is stable and has various texture properties, and so on. Gellan gum has two types, in term of forms. One is low acyl gellan gum, i.e., the acyl groups on the main chain of gellan gum molecule are removed by a heat and base treatment, either completely or partially. The other is native gellan gum, i.e., high acyl gellan gum. The high acyl type gellan gum can form soft, elastic, but not brittle gels while the low acyl type gellan gum can form firm, non-elastic, but very brittle gels. Gellan gum can work as a gelling agent with the proviso that it must be dissolved completely in water to form an aqueous solution of colloid.
Many hydrophilic colloids do not show good colloid properties in some circumstances due to incomplete dissolution. In an actual production, a lot of users can not use gellan gum properly for not knowing the dissolution property well. So, among the factors that influence the gelation property of gellan gum, it needs to firstly pay attention to the dissolution of colloid.
The dissolution process of gellan gum comprises two steps. Firstly, the gellan gum is evenly dispersed in cold water, and then heat is given to the mixture so that gellan gum can hydrate with water molecules to form gellan gum solution, thereby reaching the status of complete dissolution.
In the food industry, the even dispersion of hydrophilic colloid is very important. In a production, it needs a large amount of agitation treatment sometime so that the formation of “fish eyes” can be avoided due to incomplete hydration caused by colloid aggregations, agglomeration, or swelling effects. In the operation of food industry at present, in order to make low acyl gellan gum have a good dispersivity, the gellan gum may be firstly mixed with a chelating agent, white sugar or other powders as adjuvant, vegetable oils, propylene alcohol, and the resultant mixture is then plunged into cold water, if the formulation and the processing condition for production allow. This treatment can seclude the fine and small grains of gellan gum and reach the effect of the even dispersion in water. However, some specific foods do not use other aiding materials, and this will significantly influence the property of dispersivity of low acyl gellan gum.
The temperature of hydration for low acyl gellan gum with water is very sensitive to the ions existing in the environment, especially to divalent cations. If the low acyl gellan gum has been admixed with salts, it can only be partially hydrated with cold deionized water. The further hydration of this colloid will be blocked by divalent cations, in other water quality environment, for example, in solid water. Hereby, for the colloid, it is a must of adding a chelating agent, or heating, or both of the two methods as mentioned, to reach a full hydration.
Therefore, we can see that it needs to ensure a complete dispersion and a complete hydration of low acyl gellan gum during the dissolution process. If both of the two conditions as mentioned above can not be satisfied or only one of them can be satisfied, the following circumstances will appear, including a largely reduced gel property, a bad gel texture not reaching the ideal requirement, and so on. But, for the food-level low acyl gellan gum produced in industrial and large-scale production at present, the dissolution property has a large defect. The main deficiencies are embodied in: 1. The product has a very bad dispersivity. It can easily form aggregations during the alone dissolution process in cold water. There is a must of high speed agitation or incorporation of other adjuvant powders by a dry mixing so that the dispersivity property can be improved. If the formulation does not contain other powdery components or the operation does not allow the introduction of a high speed agitation, the low dispersivity of the product will heavily influence the ensuing treatments. 2. The product has a poor hydration property. To ensure a full hydration with water, the 0.5% solution of low acyl gellan gum product in water needs to be heated to a temperature above 80° C., and maintained at the temperature for 5 minutes. If a food formulation contains a thermo-instable adjuvant, this operation will heavily influence the property of this adjuvant. In addition, for some specific food stuff, it needs to keep the temperature during the processing conditions in production at the normal temperature. That is to say, the processing temperature needs to be kept at a temperature below 35° C. For a food product of this type, the low acyl gellan gum having the general properties will have no use. So, it will be a large promotion in applications of gellan gum in food industry if a low acyl gellan gum having high solubility is produced and provided.